<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div {
            margin: 50px  100px;
            border-style: dotted;
            border-width: 5px;
            width: 300px;
            height: 200px;
            padding: 50px;
        }
    </style>
</head>
<body>
    <!-- 盒子模型分为content,padding,border,margin -->
    <!-- padding,border会影响盒子的大小 -->
    <div>我是盒子</div>
</body>
</html>